MW: 371.3. Purity ≥98% by TLC. Background: Cell-permeable. An irreversible ubiquitin-activating enzyme (E1) inhibitor (IC?? < 10 muM). Blocks ubiquitylation and prevents ubiquitin-mediated proteasomal degradation. Inhibits NF-kappaB activation, blocks degradation of p53, increases p21 levels and induces apoptosis in vitro. Also causes an increase in sumoylation of proteins.